设x1 x2∈（0,正无穷大）且x1＜x2∴f（x1)-f(x2)=x1-x2+k/x1-k/x2=x1-x2+（x2-x1）*k/(x1*x2)=（x1-x2）*（1-k/(x1*x2)）x1-x2＜0,当x1*x2＜k时,令x1趋近x2,即x2＜=根号k,1-k/(x1*x2)＜0f(x1)-f(x2)＞0,∴f(x)在（0,...